The adipocyte fatty acid-binding protein aP2 has been shown to be essential, in mice for the development of obesity-induced insulin resistance, a frequent pathological condition strongly associated with diabetes mellitus in rodents and humans. The research outlined in this proposal is aiming at understanding the biological role of aP2 and the way it contributes to the pathogenesis of insulin resistance. Very little biological evidence has been provided so far for the functions of aP2 or other fatty acid-binding proteins. Recent evidence from aP2 deficient (aP2-/-) mice indicates strong alterations in fatty acid metabolism as well as expression of genes involved in lipid metabolism. In order to study aP2 function in a suitable experimental system, adipocyte cell lines were established from wild type and aP2 -/- embryos. In these cell lines, selected parameters of fatty acid metabolism (lipolysis, incorporation of fatty acids, lipoprotein lipase and prostaglandin synthesis) will be investigated. Also, fatty acid-regulated gene transcription will be studied by measuring the activity of peroxisome proliferator activated receptors and the dependence of them on fatty acid and synthetic ligands. A crucial role of aP2 in all of the parameters tested will be confirmed by reexpressing aP2 in the aP2 -/- cell line using retro viral gene transfer. Expression of mutagenized versions will ten be use do perform a structure function analysis of aP2. Mutations affecting ligand binding, ligand transfer to phospholipid membranes, tyrosine phosphorylation and (putative) nuclear localization will be used for this study. The physiological significance of results will be tested in aP2 -/- and wt mice for those functions experimentally accessible in vivo.